The present application is based on Japanese Patent Applications No. 2001-076396 and 2001-109555, which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a liquid-crystal display apparatus having substrates which are little bent and hardly broken by pressure so that a display image is little disordered.
2. Description of the Related Art
A liquid-crystal display apparatus (hereinafter also abbreviated to xe2x80x9cLCDxe2x80x9d) is used in a desktop electronic calculator, an electronic clock, a personal computer, or a word processor. The demand for the liquid-crystal display apparatus has increased rapidly in recent years. The application of the LCD has been widened. Reduction in thickness and weight of a liquid-crystal display panel has been required with the popularization of portable information apparatuses such as a cellular phone and a PAD in recent years. Accordingly, the LCD as a whole needs to be as thin in thickness as possible and as light in weight as possible. Further, it is preferable that the LCD is hard to break because, in most cases, the LCD has been used for portable purposes in recent years.
In the liquid-crystal display apparatus, upper and lower transparent substrates as constituent members of the apparatus were equal in thickness to each other. If reduction in thickness and weight was attended to be attained, the upper and lower transparent substrates were too thin to obtain sufficient stiffness against external force. For this reason, there was a problem that the cell gap varied to cause disorder of a display image when pressure was applied on the upper transparent substrate.
In order to make the strength against external force sufficient, the upper and lower transparent substrates needed to be made thick. This attempt was, however, contrary to the purpose of reduction in thickness and weight of the LCD. On the other hand, when the transparent substrates were made thin and impact was applied on the LCD, there was another problem that the LCD was easy to break.
On the other hand, as a reflection type LCD (liquid-crystal display) apparatus which can used both in an external light mode and in an illumination mode, there is heretofore known an apparatus using a front light system in which a side light pipe is disposed on a visual side surface of a liquid-crystal display panel so that display light can be viewed through the light pipe (Japanese Patent Laid-Open No. 147499/2000). The side light pipe, however, needs a plate thickness of about 2 mm or greater because of necessity in light transmission. Hence, there was a problem that increase in thickness and weight of the liquid-crystal display apparatus could not be avoided. Therefore, reduction in thickness and weight is an important issue particularly in a reflection type liquid-crystal display apparatus used in a portable system such as a portable personal computer or a cellular phone. In a thickness and weight reducing system in which cell substrates in a liquid-crystal display panel are made thin, there arises a disadvantage in that the panel is easy to break because of deterioration of mechanical strength.
An object of the invention is to provide a liquid-crystal display apparatus which is thin in thickness, light in weight, hard to break and easy to view.
The invention is devised on the basis of the knowledge that the stiffness of a liquid-crystal portion is determined by the stiffness of upper and lower transparent substrates of an LCD because each of the transparent substrates is bonded only around its circumference, and that the lower transparent substrate may be thinner than the upper transparent substrate because a large part of pressure is applied on the LCD particularly against the front surface thereof, that is, because pressure is little applied on the lower transparent substrate.
That is, in accordance with the invention, there is provided a liquid-crystal display apparatus having a liquid-crystal cell, the liquid-crystal cell including a lower transparent substrate having a transparent electrode on at least one of its opposite surfaces, an upper transparent substrate having a transparent electrode opposite to the transparent electrode of the lower substrate, and liquid crystal held between the lower substrate and the upper substrate, wherein the upper substrate is thicker than the lower substrate.
In order to achieve reduction in thickness and weight of the liquid-crystal display apparatus according to the invention more effectively, it is preferable that the thickness of the lower substrate is not larger than ⅔ as large as the thickness of the upper substrate.
In order to make the liquid-crystal display apparatus according to the invention harder to break, it is preferable that the lower substrate is constituted by a member having flexibility.
Assume two cases in the liquid-crystal display apparatus as follows. One is the case where the thicknesses of the upper and lower transparent substrates are equal to each other and, for example, each of the thicknesses is 0.6 mm. The other is the case where the total thickness of the upper and lower transparent substrates is equal to that in the former case and, for example, the thickness of the upper transparent substrate is 1.0 mm and the thickness of the lower transparent substrate is 0.2 mm. In the case where the thicknesses of the upper and lower transparent substrates are equal to each other, the strengths of the two substrates are also equal to each other. In the case where the thicknesses of the upper and lower transparent substrates are-different from each other in the same manner as in the invention, the strengths of the two substrates are also different from each other. When the same material is used to form the upper and lower substrates, the thicker substrate has stronger stiffness so that strain of display can be reduced.
As described above, the LCD is, however, often used in the environment that pressure is mainly applied on the upper transparent substrate. Accordingly, stiffness in the case where the upper transparent substrate is made as thick as 1.0 mm is stronger than that in the case where the thicknesses of the upper and lower transparent substrates are equal to each other. Hence, strain in the former case is smaller than that in the later case. When the same material is used, the thinner substrate is more advantageous in flexibility. Hence, the lower transparent substrate has larger flexibility as its thickness is thinner, so that the lower transparent substrate can follow bending of the upper transparent substrate, and, accordingly, can act in the direction of further reducing the influence of the bending on the whole display.
From the description, in the case where the thicknesses of the upper and lower transparent substrates in the liquid-crystal display apparatus are equal to each other, each of the thicknesses needs to be 1.0 mm and the total thickness needs to be 2.0 mm in order to obtain the same strength as that in the case where the upper transparent substrate is 1.0 mm. However, when the upper transparent substrate is made thicker than the lower transparent substrate, sufficient strength can be obtained even in the case where the total thickness is kept constant. Accordingly, when the upper transparent substrate is made as thick as possible and the lower transparent substrate is made as thin as possible relative to the total thickness of the liquid-crystal display apparatus, strain and disorder of a display image can be reduced.
According to the invention, there is also provided a reflection type liquid-crystal display apparatus having: a reflection type liquid-crystal display panel; at least one illuminator; and an optical path control layer, the liquid-crystal display panel including a liquid-crystal cell and a reflection layer, the liquid-crystal cell having a back side cell substrate, a visual side cell substrate, and a layer of liquid crystal, the back side cell substrate being made of a support substrate at least having an electrode provided thereon, the visual side cell substrate being made of a transparent substrate at least having a transparent electrode provided thereon, the transparent substrate in the visual side cell substrate being thicker than the support substrate in the back side cell substrate, the layer of liquid crystal being held between the back side cell substrate and the visual side cell substrate with their respective electrodes disposed opposite to each other, the reflection layer being provided at the back of the liquid-crystal layer in the liquid-crystal cell so that external light incident on an outer surface of the visual side cell substrate is reflected by the reflection layer and so that display light transmitted through the liquid-crystal layer is made to exit from the visual side cell substrate so as to be viewed, the illuminator being disposed on at least one of side surfaces of the liquid-crystal display panel, the optical path control layer having a thickness of in a range from 10 to 300 xcexcm and provided with light exit portions on the outer surface side of the visual side cell substrate, the light exit portions having optical path changing slopes by which light incident on the side surface through the illuminator is reflected toward the back side cell substrate, each of the optical path changing slopes being inclined at an inclination angle of from 35 to 48 degrees with respect to a reference plane of the liquid-crystal display panel.
According to the invention, it is possible to form a front light mechanism in which the optical path of incident light from an illuminator disposed on one of side surfaces of a liquid-crystal display panel is changed to a viewing direction of the liquid-crystal display panel efficiently through light exit portions of an optical path control layer disposed on the visual side and through a reflection layer disposed on the back side so that the light can be used for liquid-crystal display and in which liquid-crystal display can be performed also in an external light mode using incidence of external light. Accordingly, because of the optical path control layer sufficiently thin and the illuminator disposed on the side surface of the panel, it is possible to obtain a reflection type liquid-crystal display apparatus which can be reduced well in thickness and weight, which has the panel hard to break, which is excellent in display quality and which can be used both in an external light mode and in an illumination mode.
That is, in accordance with the invention, incident light from an illuminator disposed on one of side surfaces of a liquid-crystal display panel can be supplied to an optical path control layer while transmitted efficiently through cell substrates of the liquid-crystal display panel, particularly through a visual side transparent substrate. Hence, good emission of light can be achieved even by the optical path control layer considerably thinner than the liquid guide plate. Moreover, the visual side transparent substrate is made thicker than the back side support substrate. Hence, the quantity of light incident on a side surface of the visual side transparent substrate can be increased compared with the case where the thickness of the visual side transparent substrate is made equal to that of the back side support substrate. Hence, display light can be made brighter and the stiffness of the visual side cell substrate subjected to pressure easily can be enhanced so that a display image can be prevented from being disordered due to bending of the visual side cell substrate caused by external light. Hence, it is possible to provide a liquid-crystal display apparatus that is hard to break even in the case where the apparatus has substrates with a total thickness equal to that in the case where the substrates are equal in thickness to each other.
In addition, the light exit portions provided in the optical path control layer have optical path changing slopes each inclined at a predetermined angle. Hence, light incident on the side surface or transmitted light thereof is reflected by the slopes so that the optical path of the light can be changed with good directivity. Further, the optical path of light exhibiting a peak in a direction of regular reflection is controlled so that directivity favorable for display, particularly frontal directivity, can be provided easily. Hence, it is possible to achieve bright liquid-crystal display in an illumination mode. Also in an external light mode, external light can be efficiently taken in the apparatus by use of flat portions other than the optical path changing slopes in the optical path control layer. Hence, it is possible to achieve bright liquid-crystal display in an external light mode as well as in an illumination mode.
Features and advantages of the invention will be evident from the following detailed description of the preferred embodiments described in conjunction with the attached drawings.